W. Cross—Sanidine and Topaz from Colorado. 95 
At one point in the mountain, the nevadite, here unusually 
coarse-grained, was found to contain many small, round 
irregular druses lined by minute but perfect transparent crys- 
tals, chiefly of sanidine and quartz. 
referred to takes place. The adjoining 
cut represents one of these crystals, a ; 
normal Carlsbad twin with a third and smaller plate, also 
i twin position. The faces shown are: J (110), 7-2 (010), 
O(001), 1-2(101) and 2:7 (201) as indicated. From all the out- 
lines and from basal cleavage or irregular fissures run dar 
lines, in uniform direction for each individual of the twin, and 
the clino-pinacoid. Assuming the axial ratio 
BGs 
@:6:¢= 0°653:1:0°552 and #= 64° 
as determined by Striiver* for free crystals of sanidine, the face 
corresponds closely to 1,5.-7 (15°0-2). This would require an 
i! : 
the crystal figured was 72° 53’, Of course this can not be 
regarded under the circumstances as anything more than an 
he arpa determination. 
* Cited by Tschermak, Lehrbuch der Mineralogie, 1883, p. 455. 
